Electrostatic dust sampler



Jan. 5, 1943. e. w. PENNEY ETAI 2,307,602

' ELECTROSTATIC DUST SAMPLER v Filed Oct. 20, 19:58 a Sheets-Sheet 1wad/K. 2W

' ATTORNEY Jan. 5, 1943.

G. W. PENNEY ETAL ELECTROSTATIC DUST SAMPLER' Filed Oct. 20, 1938 3Sheets-Sheet 2 WITNESES: 9%. 16 M4. ,amfl/ae 7a,

G f lNVENTOR- e/me ATTORN'EY Patented Jan. 5, 1943.

Gaylord W. Penney Barnes, Edgewood, Pa,

Wllkinsburg, and Edgar C.

assignors to Westinghouse Electric 3; Manufacturing Company, EastPittsburgh, Pa., a corporation of Pennsylvania Application mm 20, 1938,Serial No. 236,022

22Claims.

Our invention relates generally to a device or apparatus forelectrostatically precipitating particles of dust, fumes, smoke and thelike from a gaseous atmosphere, and more particularly to a device orapparatus capable of being employed as an instrument for qualitativelyor quantitatively determining the particulate matter in the atmosphere,a process more commonly known as dust sampling, the term dustincludingany and all kinds of particulate matter that may be present in theatmosphere being analyzed.

Our invention has application for the sampling of the dust content ofthe atmospheres encountered in difierent localities or in diverseindustrial fields of which foundries, mines and pottery works areoutstanding examples, but is of general application wherever someaccurate analysis of the dust content in the gaseous atmosphere isdesired. It is aprimary purpose of our invention to design a dustsampler of general utility, and capable of use with practically anygaseous atmosphere, as for example, atmospheres in smelters or brassfoundries containing lead fumes, mine atmospheres, sooty atmospheres,foundry atmospheres containing mixtures of silica and iron pxide.Atmospheres in many localities and of many kinds have been successfullysampled with our novel instrument with consistent results with repeatedtests. Since gaseous atmospheres vary greatly in composition andconstituents, for the sake of brevity and simplicity, the term -air ishereinafter employed as'a general designation for any gaseousatmoscollapsible tube upon Our invention is, therefore, also animportant adjunct for complete dust sampling and analysis.

One of the main accomplishments of our invention is a simply andeconomically constructed dust sampler which is self-contained in acompact unit that can be easily transported from place to place, and tothis end the essential parts of the dust sampler are built into orcontained in a small case having a handle ,by whichit may be easilycarried. Inasmuch as electrical precipitation requires high voltage, thecase includes a built-in, appropriately-designed power-pack, and tofurther make the dust sampler complete in itself, a blower, comprising afan and motor, for moving air through the precipitator head, is alsobuilt into the container case. Additionally, a which the precipitatorhead may be mounted extends from the fan inlet, and

.includes a flow-measuring instrument of any suitable form by which theflowof air through the collector head may be measured.

The case compactly accommodates the voltage transforming means, that is,the power-pack and phere, but it should be understood that suchterminology is not to be deemed a limitation, except where required to aspecific end.

In general, our invention comprises apparatus for moving air or the likethrough an electrostatic precipitator head unit which has ionizingelectrodes for ionizing the dust in the air, and collecting ordepositing electrodes by-which the ionized dust i made to deposit uponone or more of the collecting electrodes. The precipitator head isdesigned with the collecting electrodes easily re-' movable sothat theymay be weighed before and trodes in any easy manner for the purpose ofmaking counts of the number of particles or for determining their sizeor general composition in accordance with known dus alyzing methods.

, after each assay. A means for measuring the flow or volume of airpassing through the prethe blower means, and is also suitably designedto provide compartments into which the precipitator head and collapsibletube may be disposed or fitted when the apparatus is not in use. All theworking parts of the dust sampler, there- 'fore, are accommodated in thecase for ready portability. In one practical embodiment of ourinvention, a case containing all the necessary elements for a completedust sampler weighs approximately but 25 pounds.

' A very important feature of our invention lies in the construction ofthe precipitator head which comprises a relatively-elongated, outer,electricity-conducting tube, preferably of metal and cylindrical,concentrically disposed about an insulated, inner central electrodeconsisting of two sections. One section comprises anelectricityconducting tube somewhat over a half length of outer tube,and the other section comprises a wire of somewhat less than half thelength of the outer tube. In operation, with a high potential appliedbetween the outer and inner electrodes, with the outer tube grounded andof a polarity to act as a collector for the dust, the zone between v thecentral wire and outer tube serves for ionizing whatever dust may be inthe air flowing through the precipitator head, while that between theouter and inner tubes serves as a dust depositing or collecting zone.The outer tube, and preferably the inner electrode also, are mounted aspart of the precipitator head in such manner that they may be easilyremoved so that they may be Weighed and cleaned or otherwise utilized inaccordance with the method of dust sampling being employed. f Since thecomposition or constituents of air may vary in different localities orindustries. the particular substance for making the electrodes must becarefully selected. We have i found that the tubes made of aluminum areexceptionally satisfactory for dust sampling in most environments andunder mostconditions. However, our novel construction of theprecipitator head permits tubes of other substances to beinterchangeably used so'that where a dust sampling of air would notyield satisfactory results with aluminum either because the con- Aftermuch experiment, we have found a relationship of parts in theprecipitator head, and

voltages to be applied thereto for dust sampling which will not yieldany measurable amount of generated, ozone or oxides of nitrogen such asare usually created in high potential electrostatic fields.

tremely important, for accurate dust analyses inasmuch as all possiblechemical'reactions between the gases and the dust should be eliminated.To achieve this result, we have em-' played, in general, the principlesdisclosed in PatentNo. 2,129,783, granted September 13, 1938,

to G; W. Penney, a co-inventor of the invention described in thisapplication, and assigned to 5 the Westinghouse Electric 8:Manufacturing Company. In the dust sampler, as in. the precipitator ofthe patent, positive ionization of the dust'particles is preferablyutilized and the functions of charging the particles and collecting themare separated.

Other novel features, objects, elements and combinations of ourinvention will be apparent from the following description thereof takenin conjunction with the drawings in which:

Figure 1 is a perspective view of one specific embodiment of our dustsampler in operative position; n

Fig. 2 is a partial, phantoflt'wiew of the case, showing certainfeatures of construction and certain parts and their position irnthecase for transportation;

Fig. 3 is a top view of the control panel in the case;

Figr 4 is a side view of the control panel;

Fig. 5 is a sectional view of a section of the collapsible tubeconnecting the blower to the precipitator head, which section isemployed .as

part of the fiow measuring device;

Fig. 6 is an axial section through the precipitator head;

Fig. 7 is a sectional view on the line VII-VII of Fig 6;

Figs. 8, 9 and 10 are schematic wiring diagrams showing different formsof power -packs for, obtaining the high voltages to be applied 'to theelectrode of the precipitator head; and,

Fig. 11 is a sectional view, on a smaller scale, showing a modified formof outer electrode.

The absence of these gases is ex- As aforesaid, it is a primary objectof our invention to have the essential parts of the dust samplerinstrument contained in a small portable case, and to this end a case 2is provided having a handle 4, by means of which it may be carried, anda hinged cover 8 which may be opened, as shown in Fig. 1,- when the dustsampler is to be used as such, or which maybe closed, and locked bymeans of a latch 8.

The essential parts of the dust sampler may be contained in the case 2and comprise the complete precipitator head 18, shown more in detail inFig. 6, a collapsible tube I2, a blower l4 and a suitable power-pack,together, with circuit controlling devices. Generally, the blower drawsthe air to be sampled through the head It and down the collapsible tubesystem, in its extended position, to an inlet of the blower from whenceit is subsequently ,discharged within the case 2. The power-pack servesto supply the' necessary voltage to establish the electrostatic fieldbetween the electrodes of the precipitator head, so that the dust willbe deposited upon the collecting electrodes during the flow of airthrough the precipitator head.

The blower and power-pack are preferably permanently built into the case2, and may be arranged therein in any suitable manner'which will yield acompact assembly whereby the case 2 may be kept to a minimum size. Theembodiment of Fig. 1 is constructedwith a power-pack shown schematicallyin Fig. 8 which' requires tworectifier tubes l6, andother'ap'purtenances in the form of transformers, condensers andresistances, and which will later be described in somewhat greaterdetail. Whatever form the power-pack.assumes, it is obvious that theparts may be compactly arranged in the lower part of the case 2 and alsoon the back-side thereof.

The blower l4 comprises an electric motor l8 driving an air moving meanssuch as a fan, and generally indicated by the reference numeral 20.

The blower has an intake 22 and a discharge outlet 24. The blower ispreferably secured in the lower, forward portion of the case 2 by anysuitable number of securing means, such as brackets 26. i

The collapsible pipe system by which air is conducted from theprecipitator head III to the blower l4 comprises a plurality oftelescoping sections, the lower one 28 of which is permanently securedto aside of the case 2 by means'of brackets 30. The tube section 28 hasa protruding stub 32 at right angles thereto aligned with the inlet 22of the blower and an adapter connection 34 completes the passage for theair flow from-the pipe 28 to the blower. The lower end of the tube 28rests on the bottom of the case, and is preferably closed by a plug, orotherwise, to prevent air from being sucked into the blower from thisend.

The collapsible tube system l2 also comprises a number of tube sections36, 38, 40 and 42, respectively, with the tube sections 36, 38 and 40 ofdecreasing size so as to be capable of nesting in a telescopic manner,and these last three secan obvious manner. In Fig. 1- the tube system isshown extended with the lower end of the sec- .tion 88 nesting in theupper end of the section 28, the lower end of the section 38 Fnesting inthe upper end of the section", and the lower end of the, section 40nesting in the upper end of v for adequately resisting the screws 44.

It is quite obvious that any number of S616? scopic sections may beprovided for the tube system I2, or any other form of collapsibleconstruction employed wherein the diflerent-tube sections areappropriately fitted together, and, as a mat-- ter of fact, in oneembodiment, instead of using telescopic tube sections, sections areemployed that can be interlocked by suitable threaded portions at eachof their ends. The whole. purpose of the collapsible tube system ismerely to enable the collector head to be disposed at a suitable heightabove the case 2 so that the air discharge by the blower will notrecirculate through the collector head and so that the collector headcan be conveniently placed at a suitable location for sampling.Manifestly, many expedients may be employed to accomplish this resultwhich is achieved by separating the intake of the collector head fromthe discharge of the blower.

The collapsible tube system I2 also includes,

in this embodiment, an air flow measuring means comprising the tubesection 42, which has a central orifice 41. During air flow thediflerential pressure-between both sides of the orifice is meas--connected by means of tubes 49 to the stub pipes in terms of thedifferential pressure or, as will subsequently be described, directly interms of cubic feet of air flow per unit time. The tube section 42 is ofsuch diameter that its lower end will fit around the upper section 40 ofthe col-- lapsible tube system, and its upper end will fit around aprotruding stub pipe extending from the precipitator head. Rings 52 maybe brazed or force-fitted or otherwise suitably positioned inside thesection 42 at a proper distance from its ends to provide stopping meansin the nature of shoulders against which the inserted pipe sectionsabut.

Resting upon angular ledges 53 secured to the sides of the case, andsomewhat from the top, is a control panel 54 which extends the length ofthe case and for a fraction of'its width. The panel is apertured as at58 to partially encompass the pipe 28 when the panel is in its oper-,ative position. Upon this panel are mounted control devices for startingthe blower and energizing the power-pack, and also to control the speedof the motor of the blower. The panel also has appurtenances in the tomof a stub tube 58,-.and an additional stub shaft 80, secured to thepanel by any appropriate means, and serving as a confining means for aportion of the precipitator head and the flow measuring devicecomprising the tube section 42, respectively, when they are to be storedin the case.

.As shown more particularly in Figs. 3 and 4, a switch 62 is mounted tothe panel 54 and controls the supply of electrical energy to the motorI8 of the blower I4, and a switch 63 controls the low potential inputside of the power-pack. The motor I8 is of the type whose speed may becontrolled by a variable resistance, and this variable resistance 64 ismounted on the-underneath side of the panel 54 with its control knob 88ured' by a manometer 48, the legs of which are means of this resistance64 the speedof the motor I8 and therefore the air flow through theprecipitator head I can be controlled.

The precipitator head sential part of our invention is shown withgreater detail in Fig. 6, and generally comprises an outer, tubularshell 88, which is preferably of metal. One end of the tube issubstantially l0 closed by a disk t insulating material, the

disk being held in position by a plurality of circumferentialiy spacedscrews 12. An insulator I4 is centrally secured to the disk 10 by aplurality of screws I6 extending through suitable 5 holes in the baseflange I80! the insulator and threading into suitably tapped apertures80' in the disk 'I0.- The insulator I4 is hollow and has a flat planeapex perforated with a central aperture into which a bolt snugly fitswith its .head .82 abutting. the flat underneath surface of the apex ofthe insulator and its threaded shank 84 protruding beyond the outsidesurface. The disc I0 and insulator 14 completely block the one end orthe shell 88 against air flow.

Conductively secured to the head 82 is the high voltage lead 86 of aninsulatingcable 88 coming from the power-pack,- and screwed onto theshank 84 is a solid-metallic cylinder 80. It may be observed in Fig. 6that the cylinder 90 is substantially centrally disposed in the shell 68and is conductively connected to the high potential lead 86 through thebolt upon which it is threaded. The cylinder is of some length with itsouter diameter accurately machined so that the can- 5 tral electrodecomprising a tube 92 may slidably and snugly fit thereover, and bemaintained, in position thereby.

The tube 92 has its end 94 spun to a' symmetri- 1 cal bullet-nose shape,and a wire 96'extends from the tip thereof, being sealed thereto in agastight manner. The tube 92 and the wire 96 com- -by an outer tubularelectrode 98 of somewhat larger diameter.

The electrode 98 is also removably mounted with respect to the remainingparts of the precipitator head, and for this purpose the other end ofthe shell 68 is'snugly fitted with an annular sleeve or closure I00,maintained in position by 50, circumferentially spaced screws I02. Asecond annular sleeve member I04 is spaced inwardly of the sleeve I00and is secured to'the shell 88 by circumferentially spaced screws I06.This sleeve member I04 is formed with a shoulder having a flat bottomside.I08 and a cylindrical side IIO extending outwardly therefrom. Thediameter or the central aperture in the sleeve I00 and of the cylinderformed by the side "0, are preferably equal, and are of a size to snuglyfit the o outer tubular diameter of the electrode-88, so

that the latter may he slid into position with its -end abutting theside I08, as shown in Fig. 6, or

may be readily removed by sliding action.

The tubular electrodes 92 and 98 are always s in set relation withrespect .to each other during operation :of the device, since thecylinder 80 maintains the inner tubular electrode 92 in poscr ew I20.The spring H6 is disposed with its 2 V directed outward in the directionof the proabove the panel, in a well known mannen'By- III which formsan' es- .prise the central electrode which is encompassed the screw Iand suitably tightening it against the shell 88 by a nut and washer onthe screw, and collectively indicated by the reference numeral I24. 3

In accordance with our invention the inside extremities of the tubes 92and 98 are placed with that of the tube 92 extending somewhat inwardlybeyond that of the tube 98. Similarly the other free extremities of thecentral electrode and the tube 98 are displaced with the end I28 of thewire 98 inward of the outer end of the tube 98.

In the operation of the collector head, air is drawn through the spacebetween the central and outer electrodes into the rear of the bodyportion I21 of the precipitator head, from whence it flows, eitherdirectly or around the insulator I4, to an outlet from the body portionwhich comprises a stub tube I28. For most successful operation, the flowof air through the precipitator head should be approximately the sameabout the central electrode. With the particular embodiment shown wehave found that an air-flow equalizer, in the form of an annular plateI29 placed about the insulator I4, and before the outlet I28 preventsa'concentration of air at the lower portion with reference to Fig. 6 ofthe preaipitator head, that is, the portions in a more direct line withthe outlet I28.

Since electrical precipitation as a rule requires a source of highpotential which is very seldom available, a power-pack forms an integralpart of'our dust sampler and can convert ordinary commercialaltemating-current voltages to constant or pulsating direct-current, orfor even greater utility the power-pack may be designed with batteriesas a primary source of energy, and,

in Figs. 8, 9 and 10, we show different power-.

packs, anyone of which may be structurally batteries I84 which supplyenergy to a voltage step-up induction coil I88 whose high voltage outputis rectified by means of a rectifier tube I88.

The power-pack of Fig. 10 is somewhat more economical than that of Fig.8 and contains fewer parts so that the total weight of the dust samplercan be somewhat decreased. The power-pack employs a step-downtransformer I40.-the'secondary output of which passes through adryrectifier I42.and is fed to the primary of a stepup induction coil I44,the output of which is made unidirectional for application to thecollector head by means of a rectifier tube I48. The circuits of Figs. 9and 10 charge the ionizing wire 98 for negative ionizationfbut theoutput connections can obviously be reversed for positive ionization.

Many electrical circuits are well-known by which high-voltagedirect-current, either con-. stant or pulsating, can be obtained fromcommercial power sources or from batteries. We do not claim anyparticular novelty in the connections of our power-pack, but do considerthe power-pack as a unit to be an important element of our invention.However, whatever type of power-pack is employed the high voltagetransformer or induction coil is preferably of the type which canwithstand a short-circuit across its secondary, such transformers beingwell known, and usually of the high-leakage type. We prefer to use ourdust sampler with substantially constant direct-current voltage betweenthe electrodes, and to this end condensers I 41 are connected across-theoutput leads of: the power-packs and are of a capacity to smooth out thevoltage ripples sufficiently for our pur- POSS.

built into the case 2, and which will yield a substantially constantdirect current voltage, Fig. 9

. employing a battery as a primary source of power and Fig. 10 beingadapted for connection to any available commercial alternating currentsource of either 25 or 60 cycles, or thereabouts.

The power-pack of Fig. 8 comprises a step-up transformer I30 withseparate low voltage secondaries for energizing the filaments of therectifier tubes I8 and the high voltage secondary I82 for connection tothe electrodes of these tubes. The circuit of Fig. 8 is well known andcorresponds substantially to that shown in the aforeaforesaid PenneyPatent No. 2,129,783 and need not therefore be described in any greatdetail, it being suflicient to state that this circuit is designed toyield a voltage in the neighborhood of 10,000 volts directcurrentbetween the ground I22 and the high potential lead 88. The connectionsshown in Fig. 8 energize the ionizing wire 98 positively; but fornegative ionizationthe connections can bechanged, along the lines taughtin the aforesaid Penney patent.

The power-pack of Fig. 9 is preferably employed in units which will beused in localities or places where no ready easily accessible source ofcommercial electric power is available, and is therefore designed toderive itsenergy from The operative position of our dust sampler isshown generally in Fig. 1.. An elongated cord I48 is adapted to pluginto any suitable outlet of a commercial frequency source, and conveyselectrical power to a power-pack of the type shown in Fig. 8 whose partsare suitably mounted in the case 2, the switch 88 controlling theapplication of power thereto. The output of the power-pack is' eitherconstant voltage or pulsating voltage direct-current, with one outputterminal or conductor preferably directed to the wire 88 of theinsulated cable 88 while the other output terminal or conductor isdirectly connected to the tube system I 2, as, for example, by aconductor I50 soldered or otherwise'conductively secured to the tubesection 28 of the tube system I2.

The cable 88 extends through a central aperture in the insulating diskI0 and the wire 88 charges the central electrode parts comprising thetube 92 and the wire 98. The other output terminal of the power-pack isconductively connected to the other electrode 98 through the metallictubesystem I2, metallic stub pipe I28, metallic outer shell 88 andspring H8. The precipitator head isnow charged for use with the? zonebetween the wire 98 and outer electrode 98 forming an ionizing chamberand the zone between the central tllbeBZ and the outer electrode 98forming a dust precipitating or collecting chamber.

The blower I4 may now be started by means of the switch 82, the speed ofthe motor being controlled by the variable resistance 84. Air willaccordingly be drawn through the precipitator head in accordance withthe arrows shown and will pass down through the extended tube system I2,through the blower. and will be disbe disposed to cover. the openportion of the case above the panel 54 to prevent the ingress of foreignmatter.

. Inasmuch as the parts of the precipitator head are carefully designedas to dimensions and the air flow outlet, it is possible to calibratethe scale of the manometer directly in cubic feet per. hour, and anydesired velocity of air may be obtained by turning the knob 66 forcontrolling the of the motor I8, and observing the reading-l ef theair-flow measuring means. 7 After a suitable run, the sampler may bedisassembled for transportation. This is accomplisliefi by firstdeenergizing all electrical circuits and pulling the plug on the cordI48, and

then removing the two electrodes from the precipitator head, leaving theremaining body portion m. This body portion may be placedlnside the case2 by inserting its stub tube I28 into the stub tube 58 on the panel 54.The tube section 42 including the manometer 'may then be removed andplaced upon an extension of a rubber cap I56 which fits the stub shaft60. The remaining tube sections 36, 38 and 40 of the pipe system maythen be collapsed into one another and 8:11 into the tube section 28.

The cable 88 is relatively short and can be folded in back of the bodyportion I54, while the cable I48 which is of considerable length,

may be wound around cleats I58 secured to the cover 6. The electrodesmay be wrapped in a cloth, or may be inserted in a small containerdesigned for the purpose, which can be disposed in the remaining spaceabove the panel 54, and

by closing cover 6 the dust sampler is ready for transportation to anyother locality where sampling of dust may be desired.

The foregoing describes only the physical steps for setting up anddisassembling the dust sampler for use. In a practical design of ourinvention the outer, grounded, metallic tube electrode 98 has an outsidediameter of 1 inches, is 7% inches long, and has a wall thickness of.035 inch, while the central tube has a V8 inch outside diameter, isapproximately 5 inches long,

and of the same wall thickness as the outer electrode. The wire 96,protruding from the central tube, is 2 inches long and of .020 inchdiameter. We have found that such proportions, when employed with adirect current potential of approximately 10,000 volts and a current of100 microamperes and over are exceptionally satisfactory for depositingdust upon the outer electrode only, and without the creation ofmeasurable amounts of either ozone or cor'iounds of nitrogen. We havetried different sizes, both of length and diameter, for the differentelements, but have finally arrived at theforegoing dimensions as themost satisfactory for accurate readings.

By means of the ground wire I22, all outside parts of the supportinghead and the outer electrode are at ground potential, and when the outorelectrode is removed, the spring IIS flexes to automatically ground thecentral electrode, and

even when the central electrode is removed the spring further flexes toautomatically ground the cylinder 90. Thus, there is practically noshock hazard in using our dust sampler. It should be noted, however,that the tip of the central elecg soot. a deposit sometimes occurs onthe tube er of tfode is at high potential when the sampler is inoperation, and should not be touched. The disposition of the end I26 ofthe wire 9 6,inwarddust. We have found that if the tip. its is placedflow measuring device disposed directly at its near or beyond the planeof the end of'the electrode 98 dust may sometimes be deposited on theoutside surface of the, electrode 98, or particleselectrode 98, it maybe brushed off or otherwise lost .when the outer electrode is removedtov be weighed, so that inaccurate results might sometimes result. Inaddition, if any particles of dust are permittedto be repelled beyondthe collecting .range of the electrodes, results may be obtained forweight, count or size sampling, or the like, of doubtful value.

Placing the other end of the tube 92 beyond that of the tube 98 is alsoa precautionary measure, and will discourage arcing or any breakdownbetween any rough points on the edges of the electrodes. a

Wehave found that electrodes made of aluminum and a wire ofplatinum-rhodium are'satisfactory for most purposes, since most dusts oratmospheres encountered will not react chemically with either of theseelements. Slight' 5 and then washed with a soap powder that containsanon-scratching abrasive to clean them thoroughly. In order to take adust sample in accordance with our invention, it is necessary to firstthoroughly clean'th'e electrodes and to dry them at least for one hourpreferably at a temperature in the neighborhood of the boiling point ofwater. However, for most accurate results the weight of each of theelectrodes before a dust sample is taken should not be determined untilthe electrodes are absolutely at thesame temperature as the surroundingatmosphere, for with each one-tenth of a degree centigrade'difference intemperature the ,error in, weight ma approximate one-tenth milligramSuch chan e in weight can be accounted for by as ingthat the air withinthe tube and a fiimjo outside of the tube tend to take the te peratureof the tube and the buoyant effect due to the change in the density ofthis vair reacts on the tube to increase or decrease its apparentweight, depending upon whether the 'tube" is cooler or warmer than theambient air.

The tubes must at all times be carefully handled and preferably by tongsor a clean cloth. After the desired run for a measured length of timethe outer electrode is carefully removed and weighed, the difference inweight before and after the run being a measure of the dust precipitatedupon the electrode. With some dusts such as the central electrode onlyon rare occasions in spite of the fact that our dust sampler has beenused with many different atmospheres contain-- ing many different typesof dust.

We have found that'with the dimensions previousiydescribed, and with anair fiow of about 3 cubic feet per minute through the collector head,all the dust in the air is precipitated, usually entirely on the insidesurface of the outer electrodeand only rarely will dust be found on thecentral electrode. Moreover, dust will not blow oil. the outer electrodeat the relatively low velocity employed. However, the speed of the motorof the blower and the total amount of sample may be controlled in caseswhere the deposited dust builds up in a light fiuify layer such as somekinds of soot may do and there is a likelihood of it being blown off byhigher air velocities.

For sampling where dust or fume concentration is very low, so that asmall change in weight of the aluminum tubes may result in aconsiderable error, or for sampling atmospheres which might react withaluminum, glass tubes with a conductaccurate results. In any event,because of the construction of our precipitator head, it is possible toreplace any of the electrodes by electrodes made of some other substancemore suitable for a particular purpose.

For sampling of air from ducts or places inaccessible to the sampler, ahose connection can be made to the outer electrode. Here again theconnection must be carefully made to avoid any possible errors in thedetermined results. A satisfactory connection may be had by wrapping asmall sheet of paper tightly around the outer end of the electrode 98and then slipping a closely fitting adapter over the paper. A goodsealcan be had between the adapter and paper with adhesive tape withoutcausing a change in the weight of the outer electrode. If the hose isclean, we have found that the foregoing precautions are not altogetheressential and may on proper occasions be dispensed with. As anotheralternative, the outer collector electrode may be formed purposely withan extension over which a rubber tube can he slipped or fitted. Anelectrode for this purpose is shown in Fig. 11 and has a body portionI60, similar in size to the electrode 98, and which is provided with anextension I62 spun or otherwise formed to a contracted cylindrical endof a diaineter more in accordance with common hose sizes.

It is, of course, imperative in our invention that the air fiowmeasuring device measure only the actual fiow between the. electrodes,and to this end the seals between the enclosures and the body sleeve 68should be made air-tight, either by the use of sealing compound orgaskets at the joints. The disposition of the air measuring meansimmediately at the outlet of the body.portion of the 'preclpitatorhead'is a further feature tending for accurate measurements, and,although we have described an orifice and manometer for the purpose, itis obvious that any other air-fiowv measuring means may be employed,

- In accordance with the foregoing we have decribed a dust samplerwhich, for all practical we face of said electrode, a second tubularelecin a unit volume ofeir can be computed" by weigh.- ing the outerelectrode in most cases, or both electrodesin some cases, before andafter a run .of predetermined time at a predetermined air 10 flow. Ifother determinations of the quality or the characteristics of the dustare required, the deposited dust may be carefully removed from theelectrode and subjected to methods for determining dust count, orsize,or composition in accordance with known practices.

.While we have described our invention in a preferred embodiment, andhave suggested certain limits in accordance with our best understandingof the same at the present time, we

no desire it to be distinctly understood that these limits are describedfor the purpose of depicting one particular form of our embodiment andnot hy way of limitation upon our invention. We

desire, therefore, that the appended claims be accorded the broadestconstruction and limited so concentrically formed and arranged inner anding glaze on them have been found to yield more trode having openingmeans permitting the passage of atmosphere through said outer electrode,said inner electrode having a closed end against the atmosphere flow,and an ionizing wire extending from said closed end but not quite to theend of the outer electrode; said head also comprising a hollow bodyportion having means for 'removably mounting said inner electrode, saidbody portion having means for removably mounting said outer electrode insubstantially gastight relation therewith so that any atmosphere flowingbetween said outer and inner electrodes discharges into said bodyportion, and atmosphere outlet means from said body portion.

2. In a device of the class described,'a precipitator head comprising atubular body portion ably secured in said body portion, closely fittingsaid opening, and extending beyond both sides of said second closure,- acentral. electrode within said tubular electrode, comprising a closedtubular member provided with an extending ionizing wire, means forsecuring said central electrode to said insulator, said body portionhaving a gas outlet, and insulated means extending through said bodyportion for conveying a potential to said central electrode.

3. The device of claim 2 including automatic means for grounding saidcentral electrode upon removal of said removable electrode.

, 4. A precipitator unit of the type describe comprising a tubular outershell, an end closure 0 therefor, a first tubulafelectrode of lesserditrode within said first electrode, means to hold said second electrodeto said shell substantially concentric with said first electrode, saidelectrodes being constructed and arranged so that when air or the likepasses through the unit, none will flow directly through the inside ofsaid second electrode, and a grounding means contacting said firstelectrode but automatically contacting said second electrodeupon removalof said first electrode.

5.. A dust sampler comprising a Drecipitator head'having outer and innertubular electrodes with contiguous dust-ionizing and dust-collectingzones operable with different potential gra-' said head, said headhaving provisions for removably supporting said collecting electrodewhereby it may be removed for weighing or other manipulation.

6. A portable, self-contained dust sampling instrument of the classdescribed comprising a case having a cover, a blower comprising a motorand fan secured in the bottom of said case, an upstanding conduitconnected to said blower, said conduit being of lower height thantheinterior of said case and secured therein, a control panel removablymounted in said case above said blower and below the top of said casethereby leaving a space thereat, a power-pack built in said caseprimarily below said panel, motor speed-control means mounted on saidpanel, comprising manually-operable means on the upper side of saidpanel, a dust precipitator head element having a stub pipe at one endthereof, a stub pipe secured to the top of said panel interfitting thefirst said stub pipe whereby said collector head may be stored in theaforesaid, space, collapsible conduit means having one extremity fittingan extremity-of the first said conduit and the opposite extremityfitting the first said stub pipe, a gasfiow measuring means in saidconduit means, said gas-flow measuring means having a removableindicator, and means on the top of said panel for mounting saidindicator in the aforesaidspace, said head having means removablyholding said outer electrode in position;

'7. A unit of .the type described comprising an ionizing chamber and acontiguous dust-collector chamber, and means for causing a gas-flowsuccessively therethrough, said ionizing chamber comprising at least onefine wire substantially spaced from a removable grounded electrode alsoforming part of said ionizing chamber; said dust-collector chambercomprising said grounded electrode, and-a second spacedelectrodesubstantially parallel to the direction of gas-flow, said wireand second electrode being insulatedly supported; relatively low-voltagepower-supply leads for the unit; limited-energy, voltage-cqnversion,

relatively high-voltage output means for unidirectionally charging saidwire andsaid inner second electrode relativelyto said groundedelectrode, said limited-energy means having such a limitedwattage-output that it"will withstand 'a short circuit, and meansconnecting ground to said tubular electrode and to one side of saidhigh-voltage output means; said last means-automatically completingaground to said insulatedparts upon removal of said grounded elec-:trode. i

a; A precipitator unit of the type-described, comprising a tubular,outer shell, an insulating end closure therefor having a relativelysmall,

is metallic and is connected to said grounded conducting member securedthereto and projecting inwardly into said shell, a tubular electrodeslidably and tightly fitting said member, said electrode beingconsiderably smaller diametrically than said shell but of a lengthprotruding outwardly therefrom, the outward end of saidelectrode beingclosed and having an ionizing wire, extending outward, a closure for theother end of said shell, thelast said'closure having a bore larger thansaid electrode, a second tubular electrode slidably and tightly fittingsaid bore, means cooperating with the last said closure for removablymaintaining said second electrode substantially concentric with saidfirst electrode, and a gas outlet from said shell.

9. A precipitator unit of the, type described, comprising a tubular,outer shell, an insulating end closure therefor having a relativelysmall, conducting member secured thereto and projecting into said shell,a tubular electrode slidably Y and tightly fitting said member, saidelectrode being considerably smaller diametrically than said shell butof a length protruding outwardly therefrom, the outward end of saidelectrode being closed and having anionizing wire extending outward, aclosure for the other end of said shell, the last said closurehaving abore larger than said electrode, a second tubular electrode slidably andtightly fitting said bore, means coopcrating with the last said closurefor removably maintaining said second electrode substantially concentricwith said first electrode, a gas outlet from said shell, and groundedsafety-means which normally makes contact with said second electrode,and with said first electrode when said second electrode is removed.

10. The structure of claim 9 wherein said shell safety-means.

"11. A precipitator uiit of the type described, comprising a'tubularouter shell, an insulating end closure therefor having a relativelysmall, conducting member secured thereto and extending into said shell,a tubular electrode slidably and tightly fitting said member, saidelectrode being considerably smaller diametrically than said shell butof a length protruding outwardly therefrom, the outer end of saidelectrode being closed and having an ionizing wire extending outward, aclosure for the other end of said shell, the last said closure having abore larger than said electrode, alsecond tubular electrode slidably andtightly fitting said bore, means cooperating with the last said closurefor removably maintaining said second electrode substantially concentricwith said first electrode, a gas outlet from said shell, and groundedsafety means which makes contact with said conducting member when bothsaid electrodes are removed.v

-12. A precipitator unit of the type described.

comprising a metal, tubular, outer shell, an in sulating end closuretherefor having a relatively small, conducting member secured theretoand extending into said shell, a tubular electrode slidably and tightlyfitting said member, said electrode being considerablysmallerdiametrically than said shell but of a length protruding'outlarger thanand wire.

13. A portable, self-contained dust sampling extending out did, aclosure for the other. end

,ofsaid shell" e last said closure having a bore trode slidably andtightly f itting-said bore, means cooperating with the last said closurefor removably maintaining said second electrode substantially concentricwithsaid first electrode, a gas outlet from said shell'i'a ground leadto said shell, means'to electrically connect said-shell and said secondelectrode, and a high-potential lead "for applying.high-ptential to saidinstrument of the class described comprising a casehaving a hingedcover, a blower comprising a motor and fan secured in the bottom of saidcase, an upstanding conduit connected to said blower, said conduit beingof lower height than the interior of said case and secured therein, acontrol panel removably mounted in said base above said blower and belowthe top of said case thereby leaving a space thereat, a--power-packbuilt in said case primarily below said panel, motor speed-control meansmounted on said panel with manually-operable means on the upidelectrode, a second tubular elec- 16. The structure oi claimcharacterized by said portion having an air-outlet, and insulated,conducting-means for conveying electric inner electrode I per side ofsaid panel, a dust precipitator head element having a stub pipe at oneend thereof, a stub pipe secured to the top of said panel interflttingthe first said stub pipe whereby said collector head may be stored inthe aforesaid space, collapsible conduit means having one extremityfitting an extremity of the first said conduit and the oppositeextremity fitting the first said stub pipe, a gas-flow measuring meansin said conduit means, having a removable indicator, and means on thetop of the said panel for mounting said indicator in the aforesaidspace.

14. A portable self-contained dust-sampling instrument of the classdescribed comprising a case and hinged cover, a blower secured in saidcase, a pipe secured in said case and connected to said blower, a dustprecipitator headhaving a hollow cylindrical body portion, an insulatingmeans closing one endof said body portion and including an insulatorattached within said body portion, of a size to leave free gas-passagesbetween said disc and body portion, said body portion having an openingat said passages, a stub pipe secured in said opening, a collapsibletube with means, for maintaining it rigidly extended, attached at oneend to an end of the first said pipe, and a section of pipe including aflow-measuring device attached to said stub pipe and the other end ofsaid tube.

15. A precipitator unit comprising a metallic,

electrode being smaller diametrically than said' first electrode anddisposed therein, the other end of said second electrode beinghollow-and fitting said tubular member whereby said second electrode ismaintained in position within said first electrode.

"- potential to said second electrode.

17.- An electrical dust-sampling instrument of the class described orgeneral application for sampling different inds of air-borne dust,comprising an electrical precipitating device having a path for the flowof a sample of air, said device including *in said air-flow pathsuccessively, an

e1 rice" ust-ionizingmeans and an electrical dus on ting means, the saiddust-ionizing means being of the type for producing ionization, with theproduction of inappreciable ozone in the presence of oxygen, saiddust-collecting means including a pair of spaced electrode means forprecipitating charged dust particles, said device including supportingmeans for individually removably supporting both said electrode means,said supporting means having aligning means for consistently supportingsaid electrode means in reproduceablepreset spaced relation, said deviceincluding means for creating an air-flow through said path, and meansfor controlling said airflow, whereby the air-iiow can be adjustedto .asuiliciently low value to prevent collected dust from blowing ofl saidelectrode means.

18. An electrical dust-sampling instrument of the class described ofgeneral application for sampling different kinds of air-borne dust,comprising an electrical precipitating device having a path for the flowof a sample of air, said device including in said air-flow pathsuccessively, an

electrical dust-ionizing means and an electrical dust-collecting means,the said dust-ionizing means beingof the type ior producing ionization,with the production of inappreciable ozone in the presence 01' oxygen,said dust-collecting means including a pair of spaced electrode meansfor precipitating charged dust particles, said device includingsupporting means for individually removably supporting both saidelectrode means I by frictional engagement, said supporting means havingaligning means for consistently supporting said electrode means inreproduceable preset spaced relation, said device including means forcreating an air-flow through said path, and means for controlling saidair-flow, whereby the air-flow can be adjusted to a sufiiciently lowvalue to prevent collected dust from blowing all said electrode means.

19. A self-contained dust-sampling instrument comprising a portablecase, a relatively small dust-precipitator head comprising an outerrelatively low-voltage tubular electrode and an inner insulatedhigh-voltage tubular electrode, said electrodes being substantiallyconcentric, and forming contiguous ionizing and dust-collecting zones,with a gas outlet connection near the end 01' said dust-collecting zone,said gas outlet connection. being conductively connected to saidlow-voltage electrode, a blower secured in said case having an intake, arelatively high-voltage-output power-pack built into said case, hav- Iing an extended, insulated, high-voltage, conductive connection to thesaid high-voltage electrode, collapsible supporting means for support-1ing said dust-precipitator head outside said case,

directed against the gas fiow, and an ionizing wire before said closedend in a direction counter to the direction of the gas flow; said outerelectrode being about said ionizing wire and cooperable therewith forproviding a dust-charging ionized field; and supporting means forsupporting said inner electrode with said tubular portion of said innerelectrode substantially rigid with respect to said supporting means, insubstantially coaxial, insulated fixed spaced relation with said outertubular electrode during dust-removing operation of the device.

21. A device of a class described comprising a dust-charging anddust-precipitating means for removing dust from a flowing gas, saidmeans comprising relatively insulated, inner and outer electrodes; saidouter electrode being a tubular electrode provided with a gas-inletopening at one end thereof, the gas flowing through said outerelectrode; said inner electrode having a tubular portion inside saidouter electrode, which is of less length than said outer electrode andcooperable therewith for providing a dust-precipitating electrostaticfield, said inner electrode comprising a closed end for saidtubularportion, directed against the gas fiow, and an ionizing wirebefore said closed end in a direction counter to the direction of thegas flow; said outer electrode being about said ionizing wire andcooperable therewith for providing a dust-charging ionized field; andsupporting means for supporting said inner electrode with said tubularportion of said inner electrode substantially rigid with respect to saidsupporting means, in substantially coaxial, insulatedfixed spacedrelation with said outer tubular electrode during dust-removingoperation of the device, said supporting means comprising means forsupporting said inner electrode only by a part of said inner electrodewhich is away from said ionizing wire.

22. A device of a class described comprising a dust-charging anddust-precipitating means for removing dust from a flowing gas, saidmeans comprising a pair of relatively insulated, inner 1 and outerelectrodes; said outer electrode being a tubular electrode provided witha gas-inlet opening at one end thereof, the gas flowing through saidouter electrode; said inner electrode having a tubular portion insidesaid outer electrode, which is of less length than said outer electrodeand cooperable therewith for providing a dustprecipitating electrostaticfield, said inner electrode comprising a closed end for saidtubularportion, directed against the gas flow, and an ionizing wirebefore said closed end in a direction counter to the direction of thegas flow; said outer electrode being about said ionizing wire andcooperable therewith for providing adust-charging ionized field;supporting means for supporting said inner electrode with said tubularportion of said inner electrode substantially rigid with respect to saidsupporting means, in substantially coaxial, insulated fixed spacedrelation with said outer electrode during dust-removing operation of thedevice, said supporting means comprising means for supporting said innerelectrode only by a part of said inner electrode which is away from saidionizing wire; said device having a gas outlet opening for gas which haspassed through said dust-precipitating electrostatic field, said Igas-outlet opening being disposed near the gasflow exit of saiddust-precipitating electrostatic field and so disposed as to cause thegas flow to curve; and gas-flow equalizing means before said gas-outletopening for causing the gas flow through the dust-charging field anddust-precipitating field to besubstantially unidirectional.

GAYLORD W. PENNEY. EDGAR C. BARNES;

